While it's generally not ideal to use decking as a shed base, primarily because it may not be strong enough to safely accommodate the weight of a shed, you can place a small, lightweight garden storage unit on it if careful considerations are met.
Why Decking Isn't Usually an Ideal Shed Base
Decking is typically designed for foot traffic and lighter loads, not the concentrated, heavy, and often static weight of a shed and its contents. There are several key reasons why it's not the best choice:
- Structural Integrity: Most decking structures are not built to withstand the heavy point loads of a shed. The joists and support posts might not be spaced closely enough or be robust enough to prevent sagging, structural damage, or even collapse over time.
- Weight Distribution: Sheds distribute their weight over a smaller footprint compared to general foot traffic. This concentrated weight can overstress specific areas of your decking.
- Ventilation and Moisture: A shed sitting directly on decking can trap moisture underneath, leading to rot, mold, and premature deterioration of both the shed base and the decking boards. Proper airflow is crucial for the longevity of both structures.
- Stability: A shed requires a perfectly level and stable base to ensure its doors and windows operate correctly and to prevent racking or twisting of the frame. Decking, especially older or less robust structures, might not provide this consistent stability.
When It Might Be Okay: Small Garden Storage Units
If you only intend to place a small, lightweight garden storage unit (e.g., a plastic storage box, a small resin cabinet for tools or cushions, or a very compact wooden unit) on your decking, it should generally be acceptable. These units are designed to be much lighter and exert less pressure than a traditional garden shed.
Key considerations for small units:
- Size and Weight: Ensure the unit is genuinely small and its total weight, even when full, is minimal.
- Decking Condition: The decking must be in excellent condition, sturdy, and well-maintained.
- Even Distribution: Place the unit to distribute its weight as evenly as possible over the decking joists.
Practical Steps and Considerations if Using Decking
If you are determined to use your decking for a shed, especially for something larger than a small storage box, significant modifications and assessments are required.
1. Assess Your Existing Decking
Before anything else, thoroughly evaluate your current decking structure:
- Check Condition: Look for any signs of rot, loose boards, or unstable sections.
- Inspect Framing: Examine the joists, beams, and support posts. Are they robust? What is their spacing?
- Determine Load Capacity: If possible, consult the original deck plans or a structural engineer to understand its load-bearing capacity. Standard residential decking is often designed for around 40-50 pounds per square foot (psf). A shed can easily exceed this.
2. Reinforce the Decking
For anything beyond a small storage unit, reinforcement is almost always necessary:
- Add Joists: Install additional joists directly beneath where the shed's footprint will sit. This increases the support density and helps distribute the weight.
- Strengthen Posts: If the shed's weight is significant, you may need to add extra support posts directly under the reinforced joist sections to transfer the load more effectively to the ground.
- Use Heavier Lumber: When adding new components, consider using larger dimension lumber (e.g., 2x8s instead of 2x6s) for extra strength.
- Create a Sub-Frame: Building a sturdy, treated timber sub-frame that sits on the reinforced decking can help spread the shed's weight more evenly.
3. Ensure Proper Ventilation and Drainage
To prevent moisture-related issues:
- Use Skids/Runners: Place pressure-treated timber skids or runners under the shed's base to lift it slightly off the decking boards. This allows for crucial airflow underneath.
- Gap Management: Ensure there are sufficient gaps between decking boards for water to drain away.
- Moisture Barrier: Consider a breathable moisture barrier beneath the shed, if appropriate, to protect the decking.
4. Consider Building Regulations and Permits
Depending on the size of the shed and your local regulations, you may require a building permit or need to adhere to specific guidelines. Reinforcing your decking might also fall under these regulations. Always check with your local planning department before starting any major work.
5. Shed Type and Size
- Smaller is Better: Opt for the smallest and lightest shed that meets your needs.
- Material: Plastic or resin sheds are generally lighter than wooden or metal ones.
- Floor System: Ensure the shed has a robust floor system that can accommodate being elevated on skids.
Comparison: Decking vs. Traditional Shed Bases
To highlight the differences, here's a quick comparison of common shed base types:
| Base Type | Suitability for Sheds | Key Advantages | Key Disadvantages |
|---|---|---|---|
| Decking | Poor (generally) | Existing structure, can be visually appealing. | Lacks strength and stability, poor ventilation, moisture issues. |
| Concrete Slab | Excellent | Extremely strong, level, durable, pest-resistant. | Expensive, labor-intensive, permanent. |
| Paving Slabs | Good (for smaller sheds) | Relatively easy DIY, good drainage, affordable. | Requires a level sub-base, can settle unevenly. |
| Timber Frame | Good (with gravel/concrete) | Good ventilation, relatively easy DIY, affordable. | Can rot if not treated, requires level ground. |
Alternatives to Placing a Shed on Decking
If your decking isn't suitable, or if you prefer a more robust solution, consider these traditional shed bases:
- Concrete Slab: Provides the most stable and durable base, ideal for larger or heavier sheds.
- Paving Slabs: A good option for medium to small sheds, laid on a compacted, well-drained sub-base.
- Timber Frame Base: A pressure-treated timber frame, often filled with gravel, offers good ventilation and can be an effective solution for many shed sizes.
Ultimately, while putting a small garden storage unit on well-maintained decking might be acceptable, placing a full-sized shed typically requires extensive and costly structural reinforcement, and often, a dedicated shed base on solid ground is a safer and more practical long-term solution.
